Expandable high-pressure flexible-tube device

ABSTRACT

An expandable high-pressure flexible tube device for sealing piping in gas or oil fields. The device comprises two end pieces interconnected by a tubular element having an elastomeric material and sheets of coils round about its longitudinal axis at a small angle of about 10° to 15° relative thereto. The sheets comprise strong helical textile cords mutually separated by a predetermined spacing. A sheet having longitudinal textile cords extends over the whole length of the device, the helical cords and longitudinal cords being imbedded in the elastomeric material.

The invention concerns an expandable high-pressure flexible-tube device,in particular for use in working underground wells, especially oil andgas wells. It is also suitable for use in other areas such as geologicalwork or mining.

In gas or oil wells, this type of device is normally used to seal wellpiping and is thus termed a "packer", which may be inflatable orexpandable. In mining, these devices are normally known as expandabletubes. Whatever the terminology used, this type of device comprises adeformable tubular membrane comprising an elastomeric matrixstrengthened by reinforcements, the two ends of which membrane are solidwith end pieces which mount the device on a mandrel for insertion intothe well or hole. These devices, which are also suitable for use inconsolidating ground by injection of cement, for measuring permeabilityby injecting water, for hydrogeological prospecting installations, etc .. . , are known in a number of embodiments, as shown, for example, in"New Generation Inflatable Packing Elements" by R. K. Mody and M. P.Coronado, presented at the "Offshore Technology Conference", Houston,Tex., May 6-9, 1991, or in French patents FR-A-2 625 254, FR-A-2 582077, FR-A-2 523 206, or U.S. Pat. Nos. 3,581,816, 5,101,908, 5,109,926,etc . . . .

When flexible-tube devices of the type described above are used inworking oil or gas fields, a non limiting example being for stimulation,they are subjected to extremely severe operating conditions as regardstemperature, pressure, chemical environment and mechanical stress.Regarding the latter, specifications sometimes require that the tubularelement composed of elastomeric material must be able to expand to threetimes its outside diameter and contract again reversibly (for example,from an initial diameter of 52 millimeters (mm) to a final diameter of162 mm and vice versa) and must resist a working pressure which can beof the order of at least 100 bars, this value corresponding to thatnecessary for pressing the tubular element against the inside face ofthe piping and to the differential counterpressures exercised on partsof the device when in this condition. The majority of known devices witha deformable elastomeric annular element--including those provided withreinforcing members--cannot completely satisfy the conditionsencountered in actual working and, as indicated in the conferencearticle cited above or in FR-A 2 625 254, the expandable tubular elementmust be combined with metal reinforcements at its ends. These must bevery carefully designed, greatly increasing the cost of the device, andthey are sometimes subject to operational malfunctions when the devicereturns to its unexpanded condition, meaning that the device cannot beused again.

The problem is thus to provide an expandable high-pressure flexible-tubedevice which does not have the problems of known devices. In general,then, one aim of the invention is to provide such a device.

A further aim of the invention is to provide such a device which, incontrast to the majority of known devices, can be reliably reused anumber of times.

A still further aim of the invention is to provide such a device whichcan seal as efficiently as known devices and in particular which pressesstrongly, when expanded, against the wall of the borehole or casingwhich is to be sealed, despite the extremely high stresses (which can beof the order of several metric tons) which occur in the zones where thetubular element is connected to the end connectors when the outsidediameter of the tubular element is multiplied by three.

A yet still further aim of the invention is to provide such a devicewhich is suitable for working gas and/or oil fields where operatingconditions comprise cycles of inflation for a short period, maintenanceunder pressure for several hours and deflation, with the deformableportion returning--to within only a few percent--to its initialdiameter.

It is known that, in order to allow the deformable portion to expand,the reinforcing members it contains must be set at a very small angle tothe longitudinal axis, of the order of 10° to 15°, and in several sheetsseparated by intermediate sheets of elastomeric material. However, thatmeasure alone does not produce satisfactory results. The prior art thusdescribes, for example in GB-A-2 099 541 or EP-A2-0 264 973,supplementary reinforcement means constituted by a plurality of helicalwindings of cords, i.e. a quantitative increase in the number ofreinforcing members whose fundamental nature is not altered. However,when that type of device is used, the multiplication in the number ofreinforcing members in the deformable annular element does not increaseperformance greatly and does not solve the problem, since the annularelement always takes the shape of a "long bone", i.e. with the endsbulging out to a greater diameter than the middle portion. The greaterdegree of inflation in these end zones results in premature bursting inthese zones.

The invention provides an expandable high-pressure flexible-tube device,in particular for sealing piping in gas or oil fields, comprising twoend pieces and a tubular element composed of elastomeric materialcomprising at least two sheets of cords wound in a helix about thelongitudinal axis of said element, at a small angle of about 10° to 15°relative to said axis, the sheets being crossed relative to said axis,characterized in that each sheet is stranded and comprises, in the warpdirection, very strong textile cords, in particular composed of aramidfibers, mutually separated by a predetermined spacing, and which areembedded in said elastomeric material by being strongly bonded thereto,the device also comprising at least one sheet of longitudinal cordswhich extend over the whole length of the device and which are embeddedin the elastomeric material of said element by being strongly bonded tosaid material.

According to a further feature of the invention, the stranded sheetsforming the reinforcing members of the expandable tubular elementcomposed of elastomeric material comprises, in the warp direction, verystrong textile cords, advantageously composed of aramid fibers such asKevlar (a trade mark of Dupont de Nemours) wherein each cord iscompletely covered with said elastomeric material and rendered highlyadherent thereto, adjacent cords not being in contact with one another.

In a further feature of the invention, the spacing of adjacent cords ispredetermined and is held at a substantially constant value duringmanufacture of the device, for example using positioning means such asmetal combs or analogous means.

The use of textile cords, in particular composed of aramid fibers whosethermal conductivity is far lower than that of steel, also means thatthe device of the invention (in which the weight of the cords issubstantial) has a higher thermal insulating power than that of knowndevices and thus a lower operating temperature in the device interior,meaning an increase in its lifetime.

In a device of the invention, in which the reinforcing members of thetubular element are yarns or cords in stranded sheets--pressuresheets--, inflation of the tubular element causes the yarns or cables tomove further apart by elongation of the elastomeric material between twoadjacent yarns or cords, along with a small angular deviation of theyarns or cords from the initial positioning of about 10° to 15° in theunstressed state of the device, inflation occurring at a lower pressurethan with known prior art devices.

According to a further feature of the invention, the sheet oflongitudinal cords is stranded and the longitudinal cords are spacedapart by a predetermined distance.

Further, the sheet or sheets of longitudinal cords may be close to theouter periphery of the tubular element, and/or close to the innerperiphery, and/or between two pairs of crossed cord sheets, and/orbetween crossed cord sheets.

In an embodiment of the device, each sheet is composed of 3300/1/3 dtexaramid fibers (i.e. cords containing three twisted yarns, eachmonofilament yarn having a numbering of 3300dtex) treated by rolling orcoating with an adherence-producing substance composed ofpolychloroprene, for example.

With this type of structure, and in contrast to known devices, the cordsdo not stretch, meaning that they can return to their initial positionafter deflation, encouraging a return by the device to its initialdiameter.

In a variation of the invention, in order to reduce the stress close tothe ends of the expandable tubular element, the stranded pressure sheetsare conformed such that the angle of the yarns or cords constitutingthese sheets is different in said end zones to that in the middle zoneof the tubular element.

In one embodiment, the laying angle for the yarns or cords constitutingthe pressure sheets is of the order of 10°-12° in the middle zone, wherethe element has to expand by up to three times its initial diameter, andis of the order of 20° in the end zones.

In a further variation of the invention, stress close to the end zonesis limited by attaching sleeves with reinforced borders to these zones,which sleeves, after positioning, are turned back then fixed withlongitudinal ties.

In a still further variation of the invention, a winding of radiallydeformable fabric is used to reduce stress in the end zones of thedevice.

Further characteristics and advantages of the invention become apparentfrom the following description made with reference to the accompanyingdrawings, in which:

FIG. 1 is a highly schematic view of a device of the invention;

FIG. 2 shows two devices of the invention in the expanded state as theywould used in an operation of stimulating an oil well;

FIG. 3 is a partially cut-away view of the basic structure of adeformable annular element of a device in accordance with the invention;

FIG. 4 is a section along line 4--4 in FIG. 3;

FIG. 5 is a highly diagrammatic perspective view of a device inaccordance with the invention;

FIG. 6 is a highly diagrammatic view of a further embodiment of theinvention illustrating an advantageous disposition of the yarns or cordsof a reinforced pressure sheet, in the rest position;

FIG. 7 is a diagrammatic view illustrating the deformation of an annularelement in a known device;

FIG. 8 is an analogous view to FIG. 7, for a device in accordance withthe invention;

FIG. 9 is a view analogous to FIG. 3 but for a preferred embodiment ofthe invention;

FIG. 10 is a section along line 10--10 in FIG. 9.

Referring firstly to highly diagrammatic FIGS. 1 and 2 whichrespectively show an expandable high-pressure flexible-tube device andan example of the use of such a flexible-tube device in working oilfields. The expandable high-pressure flexible-tube device or "packer" 10comprises an expandable tubular element or membrane 11 composed of anelastomeric material, fixed at its two ends 12 and 13 to respective endpieces 14 and 15. These end pieces are advantageously as described inour European patent EP-A1-0 516 515, however this is not limiting in anyway.

When such devices or packers are used for stimulation in an oil well,two devices 10a and 10b with an outside diameter in the unexpanded statewhich, in one embodiment, may be about 54 mm, are mounted on a mandrelM, are lowered through production tubing of slightly larger diameter,and are placed on either side of a production zone pr of well P. Devices10a and 10b are then expanded to isolate a zone z into which acid sludgeis injected to stimulate the production zone, using suitable means whichare not shown. The diameter of the well or its casing is, in some cases,of the order of 162 mm, so that in order to obtain a satisfactory seal,membrane 11 must be expanded to about three times its initial diameter.It must also be able to withstand high pressures of the order of atleast 100 bars, i.e. an inflation pressure of the order of 30-40 barswhich presses the membrane against the casing, and differentialcounterpressures exercised on different parts of the membrane which canbe of the order of 60 bars or more, all in a difficult environment(working temperature in the range 20° C. to 120° C., humidity which canvary from 0% to 100% between storage and use, and the presence of heavyhydrocarbons and chemical substances which are acidic and corrosive).

In order to produce an expandable high-pressure flexible-tube devicewhich can be used under these conditions, according to the inventionmembrane 11 (fixed at its ends to end pieces 14 and 15, the first ofwhich is movably mounted in known fashion on mandrel M) is constitutedby a matrix of elastomeric material(s), advantageously a mixture ofrubbers with excellent remanence when highly stretched and which has therequired characteristics of mechanical strength and resistance tochemical substances. At least two sets of reinforcing "pressure" membersare embedded in a matrix of this type which may, for example, be ofpolychloroprene. According to the invention, the reinforcing members arein the form of stranded sheets of textile yarns or cords, advantageouslycomposed of aramid fibers such as Kevlar (trade mark of Du Pont deNemours). As shown in FIG. 3, at least two crossed sheets 20 and 21 arepresent, the first mounted on an inner tube 22 and the second mounted onthe first with an intermediate sheet 23 between them, for example butnot necessarily of the same elastomeric material as that of inner tube22; the two sheets 20, 21--which are crossed relative to thelongitudinal axis A of the membrane--are each constituted by yarns orcords 24 for sheet 20 and 25 for sheet 21, each completely covered withelastomeric material and laid at an angle α of the order of 10° to 15°to axis A. Cords 24 and 25, which adhere strongly to the elastomericmaterial in which they are embedded, have a Young's modulus which ishigher than that of the material and they are disposed in a fashionanalogous to warp yarns in a woven fabric, being held during positioningat a substantially constant predetermined mutual spacing, for example bymeans of metal positioning combs. With this structure for the pressuresheets, inflation of membrane 11 is easy and immediate even at lowpressures, its diameter passing from its initial condition with diameterd to a value of about 3d at a pressure of between 30 and 60 bars.Further, the cords remain properly in position and return to theirinitial position after deflation, without stretching.

When this structure is combined with means which limit the stressoccurring close to the ends during inflation, then in the end zones andin its inflated condition membrane 11 has a shape close to that shown inFIG. 8, i.e. with a portion 30 in which the cross-section through alongitudinal plane is regular from the end pieces 14, 15 up to theexpanded portion of the membrane. In prior art devices without the meansof the invention, however, the shape of the membrane after inflation isthat of a "long bone", FIG. 7, where the ends have a larger diameterthan the central portion.

The means which limit the stress in the connection zones at the endpieces in the tubular element of the device in the inflated state areconstituted, in a preferred embodiment of the invention and as shown inFIGS. 9 and 10, by at least one stranded keeper sheet whose longitudinalyarns or cords 50 extend along substantially the entire length of thedevice and which are embedded in the elastomeric material constitutingmembrane 40 to which they are strongly bonded, as are the other yarns orcords 43 and 44 of pressure sheets 41 and 42, laid at a angle of theorder of 10° to 15° relative to the longitudinal axis of the membrane,the first on a central tube 45 of elastomeric material and the second onan intermediate sheet 46, for example but not necessarily of the samematerial, the two sheets being crossed relative to longitudinal axis A.

This structure for membrane 40, where longitudinal reinforcements 50are, for example, located close to the periphery 55 of the membraneconstituted by an elastomeric material tube 56, produces a "packer"which satisfies specifications for use.

Some longitudinal cords 50 can also be provided close to the insidesurface of the element, and/or between pairs of crossed cord sheets,such as the pair of sheets 41, 42, or even between two crossed sheets41, 42.

In a variation of the invention, in order to reduce the stress occurringon inflation of the expandable tubular element, in particular close toits ends, cords of reinforcing members of pressure sheets can bepositioned as shown in FIG. 6, i.e. such that they form--in theirinitial laying position--a varying angle with axis A of the membrane,for example of the order of 10°-12° in the middle zone and of the orderof 20° close to the ends which are provided with end pieces 14 and 15.With this structure, which can be produced by holding the cords captivein strips of elastomeric material of varying width and then windingthese strips appropriately, the deformation observed close to the endsof the membrane after inflation exhibits a regular transition betweenthe expanded membrane of the end pieces 14 and 15, where the diameterremains that of the membrane in its initial state.

The stress which each sheet needs to withstand can be further reduced byproviding more than two stranded sheets and by adjusting the ratiobetween the density of the reinforcing cords to the quantity ofelastomeric material in which they are embedded.

In a further embodiment, which is not illustrated, a winding of radiallydeformable fabric is positioned in each end zone of the device.

In a still further embodiment of the invention, shown in FIGS. 5 and 6,sleeves 31 are mounted near the connections of the ends of membrane 11to end pieces 14 and 15, which sleeves advantageously have reinforcedborders which, after positioning, are turned back then fixed bylongitudinal ties 32.

EXAMPLE

A membrane 40 of a device of the invention was produced from an innerpolychloroprene tube with an inside diameter of 26 mm and a thickness of4 mm on which a first stranded sheet reinforced with 3300/1/3 dtexaramid was mounted. A 2.4 mm thick intermediate sheet was mounted onthis sheet and was in turn covered with a second stranded sheetreinforced with 3300/1/3 dtex aramid. A further intermediate sheet wasdeposited over this second sheet and was in turn covered with a thirdstranded sheet reinforced with 72 cords of 3300/1/3 dtex aramid, whichwas in turn covered with a tubular coating with an outside diameter of53 mm.

Tests conducted with this "packer" achieved an inflation of 3 diametersat a pressure of the order of 50 bars, the rupture pressure obtainedbeing more than 100 bars in a 152 mm casing.

We claim:
 1. An expandable high-pressure flexible device for sealingpiping in gas or oil fields, the device comprising two end pieces and atubular element interconnecting said end pieces, said tubular elementhaving a longitudinal axis and comprising an elastomeric material andsheets of cords which are wound about said longitudinal axis at a smallangle of about 10° to 15° relative to said axis and which are crossedrelative to said axis, said sheets comprising strong helically woundtextile cords which are mutually separated by a predetermined spacing,the said device further comprising at least one sheet havinglongitudinal textile cords extending over the whole length of thedevice, the said longitudinal cords being parallel to said axis andmutually separated by a predetermined distance, the said helical cordsand the said longitudinal cords being embedded in said elastomericmaterial and bonded thereto.
 2. A device according to claim 1, whereinthe said spacing of the cords in said sheets is substantially constant.3. A device according to claim 1, wherein said sheets are composed ofcords of aramid fibers treated by rolling or coating with a bondingsubstance.
 4. A device according to claim 3, wherein the aramid fiberscords are made of three yarns twisted together, each yarn having alinear mass of 3300 dtex.
 5. A device according to claim 1, wherein thesaid angle of the cords is different in the end zones of the tubularelement from that in the middle zone of said tubular element.
 6. Adevice according to claim 5, wherein the initial laying angle of thecords is of the order of 10°-12° in the middle zone, where the tubularelement has to expand by up to three times its initial diameter, and is20° in the end zones of said tubular element.
 7. A device according toclaim 1, wherein the ends of the tubular element near the end pieces arecovered by sleeves adapted to limit the stress in the ends of thetubular element during inflation, the sleeve on one end of the tubularelement being connected to the sleeve of the other end of the tubularelement by longitudinal ties.
 8. A device according to claim 1, whereinthe ends of the tubular element comprise windings of a radiallydeformable fabric.